Urocanasa

Urocanasa, also known as urocanase, is a cellular enzyme involved in the degradation of the amino acid histidine. It catalyzes the hydration of urocanic acid (urocanate) to 4-imidazolone-5-propionate as part of the histidine catabolic pathway that converts histidine into glutamate.

In the histidine degradation cascade, histidine is first converted to urocanic acid by histidine ammonia-lyase (HAL). Urocanasa then adds water to urocanate to produce 4-imidazolone-5-propionate, which is subsequently processed by other enzymes such as imidazolonepropionase to form compounds that ultimately contribute to glutamate synthesis. The enzyme is encoded in humans by the UROC1 gene, located on chromosome 7p, and is expressed in tissues involved in amino acid metabolism.

Clinical significance: Deficiency of urocanasa causes urocanic aciduria, a rare inborn error of metabolism. The clinical presentation is highly variable; many individuals are asymptomatic, while others may exhibit developmental delay or hypotonia. Diagnosis is typically based on biochemical findings, notably elevated urocanic acid in urine, and can be confirmed by genetic testing of the UROC1 gene. Newborn screening for this condition is not routinely performed due to its rarity and variable phenotype.

Genetics and management: Urocanase deficiency is inherited in an autosomal recessive manner. There is no widely established specific therapy; management is generally supportive, focusing on monitoring, familial counseling, and addressing any clinical symptoms that arise.